The new number isn't a sign of a major upgrade. As we've chronicled, Torvalds thinks that it looks a bit silly when version numbers go beyond x.19. He therefore decided it would be best to tick over from 3.19 to 4.0 for the sake of neatness, rather than to celebrate any particular milestone in the kernel.

Which is not to say this release is devoid of improvements. Notable inclusions are the addition of non-disruptive patching, support for Intel's Quark systems-on-a-chips and better support for the Z13 silicon powering IBM's latest mainframes. A handful of new ARM chips also get support and there's the usual round of improvements and tweaks to graphics and sound performance. ®